Lysine succinylation

Figure 4.10. Dose-relationships for histamine release from rat mast cells induced by a variety of peptides [99], No calcium was added to the extracellular medium. Each point is the mean of two or more determinations A, poly(L-lysine) (molecular weight 30.000-70,000) , succinylated poly(L-lysine) (molecular weight 30,000-70f)00) V, [n-Phe7 )SP , fD-Prcr2, D-Phe7, D-Trpv]SP, u , SP/ A, eledoisin-related peptide , eledoisin O, N-terminal tetrapeptide of substance P.

Conjugate was too toxic in vivo to be effective. Succinylation of lysine side chains decreased toxicity, but eliminated anticancer effect against LS180 colon carcinoma... 

SchemelO Chemical structure ofthe polypeptide obtained after introducing spiropyran units into the side chains of succinylated poly(L-lysine) (XVII). 70 ...

It has been suggested that the modification of the protein s isoelectric point could result in an alteration of its pharmacokinetic profile. Avidin acylation was performed by lysine amino group derivatization with succinyl anhydride or other anhydrides, which allowed the isoelectric point to be shifted to more acidic values, depending on the level of modification. Indeed, the protein anionization induced a reduction of accumulation in the liver, but resulted only in a limited prolongation of residence time in the circulation [30, 31]. 

The mechanisms of modification are different and depend on the chemical molecules used for the reactions. The anhydride of succinic acid reacts with lysine residues, a-amino groups of proteins and free thiol groups. During succinylation, proteins lose their globular structure and undergo aggregation by disulfide cross-binding with other whey proteins. Acetyl anhydride can modify tyrosine residues. 

Several workers have chemically modified milk proteins ( c-casein, casein) to determine the chemical basis for the stabilization of the casein micelle by c-casein and to elucidate the mechanism of rennin action (35,36). Creamer et al. (37) made several derivatives of sodium caseinate and showed their improved solubility. In preliminary feeding trials in which succinylated casein was the only protein source, supplementation with lysine was required for the normal growth of rats. 

Nutritional Availability of Acylated Lysine and Proteins. The successful use of chemically derivatized proteins as food ingredients requires that they be digestible and nontoxic, and that the modified amino acid residues should be available nutritionally. Nutritional studies using modified food proteins are limited. The nutritional availability of several acylated lysines were studied by Bjarnason and Carpenter (105) and Mauron (106) and the results are summarized in Table III. The bioavailability of the acylated lysine varied significantly with the type of the acyl groups (see Table III). In addition acylated proteins (acetylated and succinylated) gave lower responses to the growth activity for the rats than equivalent supplements of unmodified proteins... 

Preliminary evidence from enzymatic digestion of the native 7S and 11S proteins suggests that the 7S protein may have a more hydrophilic surface than the 11S protein. Thus, trypsin digests the 7S fraction more rapidly than the 11S at pH 5.8-6.7, whereas rennin degrades the 11S more rapidly than the 7S. The epsilon-amino groups of lysine may also be more available on the surface of the 7S resulting in easier succinylation. 

Succinic anhydride reacts with free amino groups, the phenolic and thiol groups of tyrosine and cysteine. The latter esters spontaneously hydrolyze in aqueous solution (39). The e-amino group of lysine reacts most readily. Succinylation has three major effects on the physical character of proteins it increases net negative charge, changes conformation and increases the propensity of proteins to dissociate into subunits (39,40,41,42). 

Determination of the completeness of lysine acylation is performed by dinitrophenylation (Fraenkel-Conrat et al. 1955) of the succinylated protein, followed by acid hydrolysis, and amino acid analysis. Since fi-dinitrophenyllysine is stable to acid hydrolysis, the recovery of lysine reflects the -succinyllysine content of the protein. 

Little attention has been given to the biological consequences of such acylation for food use. Creamer et al. (40) reported the result of growth and toxicity trials in rats and mice fed acetyl or succinyl casein and acetyl milk whey protein. These proteins had lower protein efficiency ratios than casein, and added L-lysine hydrochloride did not correct this deficiency. However, a trial with acetyl casein in mice showed no overt toxicity. These workers (40) concluded that none of the milk proteins as modified with anhydrides can be regarded as suitable for inclusion in acidic food products. It is obvious that a thorough biological evaluation is needed to assess whether acylated soy proteins are suitable for food use. 

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